A crucial physiological parameter for the brain in hypoxemia is oxygen availability, defined as the amount of oxygen made available per 100 gm of brain per minute. We propose to make measurements of oxygen availability and local cerebral glucose metabolism in hypoxic rats to investigate the effect of oxygen delivery and its relation to local cerebral glucose metabolism. As oxygen delivery is compromised, changes in cerebral glucose metabolism will be assessed in different regions and structures of the brain. The measurements that we propose to make have been attempted by other investigators, but the techniques available to them have not been both regionally specific and quantitative thus leading to confusion and misinterpretation, even though animal models of hypoxia and hypoxia-oligemia are available and well researched. The measurements that we propose to make are now possible because of the development of a double label technique for determining both local cerebral blood flow and the cerebral metabolic rate for glucose in the same area of the same animal with the spatial detail of autoradiography. Quantitative measurement of CBF and CMRglu can be made in areas as small as cortical columns, which can be resolved with this technique. Measurements of both parameters in the same animal will answer the question as to whether the columnar organization of CMRg1 in hypoxia is flow dependent and what its relationship is to oxygen availability. The critical level of oxygen delivery below which the metabolic rate of glucose shows dramatic changes will be assessed in different regions and structures of the brain. The relationship of tissue vulnerability to this critical level will then be defined.